Firey hot, a little painful, and extremely erotic...

Nicoletta took her time with the succubus's warm body, swallowing what seemed like an impossible amount of cum. She felt dizzy for quite a while, and a little drunk, but continued to lick and torment her lover. Then, as the shaking succubus finally finished draining, her hand on her belly and her eyes heavy, Nicoletta felt a deep burn.
It wasn't quite what she was expecting. Her belly felt warm and then very hot, like it was full of molten metal. What was worse was that it was spreading. The succubus wrapped her hand around the back of her head, pulling her close against her groin, as the feeling spilled deeper and wider. Her muscles began to tense up, and buck uncontrollably, and her eyes began to tear. She tried to speak, but the massive strength of the succubus held her mouth tight against her pussy and nothing comprehensible escaped.
The heat of her belly spread in tendrils, twisting into her thighs and her abdomen, her buttocks and her back. She felt it creeping into her chest, and her breasts, where her nipples promptly became extremely sensitive and hot to the touch. It worked its way down her legs, to her feet, burning from the bones. It coursed up her spine and through her muscles to her neck, down her arms to her fingertips, and into her skull. It pressed into her brain and scalp, her face and eyes, her lips...
The heat exploded like the sun at the last second, and she screamed. This was definitely not what she was expecting, and yet... she was so wet again! She liked this. Her muscles bulged, her back ached with a growing pain like she had never felt. Her scalp developed a pair of small horns, prodding out from her forehead. A dark pair of wings slowly tore from her back, as the succubus began to laugh. She was so hot...
Her breasts became terrifically large. They were, much like the succubus's, perfectly round and so arousing Nicoletta could feel it herself. She had them, and she still wanted them. They were so... beautiful, her nipples so puffy and seductive...
She knew then that there was a catch involved. There was a strange hunger... the succubus hadn't been completely honest, had she? But how bad could it be, for a body like this one?